[throwawaaarrgh]

It's for sharing and aggregating. Ccache is useful locally, but really shines when combined with Distcc, a distributed compiler. Every host contributes a cache object that other hosts can use, and every host can use the cache object contributed by other hosts. So you don't even have to built it once yourself to benefit from the cache of everyone else. It therefore speeds up multiple hosts/users builds, distributed builds and the dev experience of individuals.